A light emitting device using a light emitting diode (LED) is widely used for optical devices such as display devices of indoor type, outdoor type, stationary type, movable type or the like, display lamps, various switches, signal devices, general lightings and the like. Out of light emitting devices using LEDs, there is known a transparent light emitting device in which a plurality of LEDs are disposed between two transparent substrates, as a device suitable for a display device which displays various character strings, geometric figures, patterns, or the like, a display lamp or the like. By using, as a transparent substrate, a flexible substrate or the like made of a transparent resin, restriction with respect to a surface to which the light emitting device as the display device or the display lamp is attached is reduced, which enhances convenience and availability of the transparent light emitting device.
A transparent light emitting device has a structure in which a plurality of LED chips are disposed between a first transparent insulating substrate having a first conductive circuit layer and a second transparent insulating substrate having a second conductive circuit layer, for example. The LED chip has a structure in which a first semiconductor layer, a light emitting layer, and a second semiconductor layer are stacked in order on one surface of a semiconductor substrate, for example. A first electrode is provided on the second semiconductor layer, and further, a second electrode is provided on the other surface of the semiconductor substrate. The first electrode is provided on the second semiconductor layer so that an area thereof becomes sufficiently smaller than an area of the light emitting layer in order not to prevent emission of light from the light emitting layer. The first and second electrodes of the LED chip are electrically connected to the first and second conductive circuit layers, respectively. In a space between the first transparent insulating substrate and the second transparent insulating substrate, a transparent insulating resin or the like having an electric insulation property and flexibility is filled.
Electrical connection of the electrodes of the LED chips and the conductive circuit layers, is realized when a stack of the first transparent insulating substrate, the LED chips, and the second transparent insulating substrate is subjected to thermocompression bonding, for example. Regarding the electrical connection of the electrodes of the LED chips and the conductive circuit layers, it is proposed to use a conductive adhesive or a hot melt adhesive, or to set a thickness of the transparent insulating resin filled between the substrates to be smaller than a thickness of the LED chips to press the conductive circuit layers against the electrodes of the LED chips. However, a conventional transparent light emitting device has a fault such that when it is bent, luminous intensity of LED chips easily reduces or non-lighting or the like due to short circuit easily occurs.